Method for compacting powdered metals



Sept 5, 1.967 I T. s. CLORAN ETAI. 3,340,056

METHOD FOR COMPACTING POWDERED METALS /N vE/vrons. v moms s. c/ ORA/v a VER/vom R. THOMPSON `United States Patent() 3,340,056 METHOD FOR COMPACTING POWDERED METALS Thomas S. Cloran, East Liverpool, Ollio, and Vernon R. Thompson, Pittsburgh, Pa., assignors to Crucible Steel Company of America, Pittsburgh, Pa., a corporation of New Jersey Filed Jan. 31, 1967, Ser. No. 613,023 6 Claims. (Cl. 75-214) ABSTRACT OF THE DISCLOSURE tainer. Axial forces are applied to the container within l `the die to 'compact the powdered material while collapsing the container. During this operation, the hemispherical ends of the container prevent the cylindrical walls from buckling during the final stages of compacting by permitting high volume (powdered metal) to container vsurface ratios.`lf buckling occurs, as is the case with cylindrical fiat-ended containers, it becomes virtually impossible to remove the container from the compact, after compacting has been completed, by conventional machining and/or pickling operations.

' In the art of powderA metallurgy, wherein metal in powdered form is subjected to a combination of elevated temperature and pressure to compact the same into a dense metal article, it is desirable to conduct the heating and compacting operation with the metal contained within a gas-tight capsule or container that has been evacuated to a pressure substantially less .than atmospheric. In this manner, oxidation' of the particles may be prevented during the heating cycle, which results in a final article of improve'd cleanliness. Forthis purpose, powdered metal to be compacted is .placed in a cylindrical container or capsule having at closed ends. The container is placed within a die conforming substantially to the cross section of the container. A plunger or ram is inserted into the die to apply an axial load to the container sufficient to collapse the same and compact the powdered metal. The material is customarily compacted to a nal density of substantially 100 percent and at least on the order of about 95 percent or greater. It has been observed that during compacting to achieve densities greater than about 80 percent, the walls of the cylindrical flat-ended container collapse inwardly or toward the axis thereof irregularly or unevenly along the length of the container. This results from the decrease in container length during compacting exceeding the diameter increase, which results in the uneven or irregular buckling of the container walls toward the axis thereof. After compacting, itis, of course, necessary to remove the container from the compacted article prior to use thereof or further finishing operations, such as forging and machining. The removal of the container from the compact is achieved by acid pickling, machining, or a combination of both operations. It is obvious that with the container walls collapsing unevenly along the length of the compact, removal of the container from the compact by these operations becomes almost 3,340,056 Patented Sept. 5, 1967 ICC impossible without destroying 'a substantial portion of the compact itself during the removal operation.

It is accordingly a primary object of this invention to provide a method of compacting powdered metals that are within a sealed container, while avoiding uneven collapse of the container walls during the final stages of the compacting operation.

Other objects of the invention, as well as a complete understanding thereof, may be obtained from the following description and drawings, in which:

FIGURE l is a perspective view of -an embodiment of a container'used in the practice of the invention, and having a portion thereof broken away to show the powdermetal charge Within the container;

FIGURE 2 is a schematic showing of a cylindrical flatended container positioned within the `die prior to being compacted;

FIGURE 3 is a similar view showing the cylindrical flat-ended container and charge compacted to a density of about percent; Y

FIGURE 4 is a similar view showing the cylindrical fiat-ended container and charge compacted to a density greater than 80 percent, whereupon the wall of the container has collapsed inwardly and unevenly along the length thereof;

FIGURE 5 is a schematic showing ofA a cylindrical hemispherical-ended container positioned in a die for compacting in accordance with the method of this invention;

`FIGURE l thereof, -there is shown a container constructed in accordance with the prevent invention. The container, designated `generally as 10, consists of a cylindrical body portion 11, whichV may be, for example, a length of mild steel pipe. Each end of the body portion 11 is closed by hemispherical cap 12 which is welded, as at 14, to the body portion 11. One of the caps 12 contains a stem 16 which permits the interior of the container to be connected to a vacuum pump for evacuation. A charge of metal particles, designated as 18, fills the container. The metal is in powdered form, e.g., mesh, and may be any desired metal or combination of metals, such as AISI M2S tool steel. In the practice of the invention, a cylindrical hemispherical-ended container lled with metal particles, as shown in FIGURE 1, is connected, as by stem 16 to a vacuum pump that reduces the pressure within the container to a level substantially below atmospheric pressure, e.g., 50 microns. The container and powder metal charge therein are heated to an elevated temperature, eg., about 2000 F., for compacting. The container 10, at elevated temperature and low pressure, is placed on end within a die 20, as shown in FIGURE 5. The walls of the die 20 conform substantially to the cross section of the container and consequently `restrict the lateral spread thereof during compacting by the application of axial force by ram 22. Prior to compacting, the density of the powdered metal within the container is on the order of 65 percent, although g-reater density may be provided. As

may be seen in FIGURE 6, as the ram 22 is lowered within the die 20, the hemispherical ends of the container are initially collapsed without causing any expansion of the cylindrical walls 11 thereof. Compacting to a powder density of about 80 percent is achieved during collapsing of the hemispherical container ends and prior to the expansion of the cylindrical walls 11. As shown in FIGURE 7, the ram 22 is further lowered within the die 20 to further collapse the container and compact the powder to a density approaching 100 percent. During compacting from an 80 percent density (FIGURE 6) to a density of about 100 percent (FIGURE 7), the corresponding diameter increase of the cylindrical walls 11 of the container are in the same proportion as the decrease in container length. Consequently, buckling of the container walls unevenly along the length thereof, as shown in FIGURE 4, is avoided. Therefore, when compacting to the desired 100 percent density has been completed and the container is removed from the die, the container may be stripped from the compact by machining or pickling, as described above, without requiring any substantial removal of the compact itself during the operation. It may be seen that this not only facilitates the removal of the container from the compact, but also adds said container from said article after compacting.

During the initial stage of the compacting operation, as described hereinabove, the use of a container having hemispherical ends (as opposed to flat ends) permits a reduction in the volume of the container and an accompanying increase in the density of the powder therein before the axial compressive compacting forces begin to act on the cylindrical walls of the container. After the initial stage of compacting, the axial force is applied to and through the powder and against the cylindrical wall of the container. This moves the wall outwardly, along the entire 360 degree circumference thereof, until such further movement is prevented by the die wall. The container wall is maintained against the die wall by the continuing pressure applied to the powder. At this stage of the cornpacting cycle, the radial movement of the cylindical wall of the container and the powder terminates and the powder is compacted to the desired nal density.

As a specific example of the practice of the invention, a quantity of AISI MZS tool steel powder of -100 mesh was charged to two, 6-inch diameter, mild steel pipes having wall thicknesses of 1A inch. One of the pipes had its ends closed by two at discs welded to the pipe ends; this will be referred to hereinafter as the flat-ended container designated as 10a in FIGURES 2, 3, and 4. The other pipe had its ends closed by two, hemispherical, mild steel caps that were welded to the pipe ends; this will be referred to hereinafter as the hemispherical-ended container, as shown in FIGURE 1. Both containers were placed in dies, as described above and shown in FIG- URES 2 through 7. Prior to being placed in the dies, of course, each container was evacuated to a pressure of about 25-microns and was heated to a temperature of approximately 2200 F. A 200G-ton press was used for the compacting operation and applied forces during compacting on the order of about 40,000 p.s.i. Both containers and their respective powder-metal charges were compacted to a powder density of 100 percent. Both-containers were removed from the dies and sectioned for examination. The flat-ended container had buckled inwardly unevenly along the length thereof, in the manner shown in FIG- URE 4. Examination of the hemispherical-ended container showed a substantial absence of buckling; the cross section of this container and associated compact were similar to that shown in FIGURE 7.

Although various embodiments of the invention have been shown and described herein, it is obvious that other modictaions and adaptations may be made by those skilled in the art, without departing from the scope and sphere of the appended claims.

What is claimed is:

1. A method for producing a compacted article from powdered metal comprising filling a cylindrical metal container having hemispherical ends with a charge of powdered metal to be compacted, applying axial compressive force to said container to compact said charge of powdered metal, restricting lateral spread of said container during said application of axial force, and removing said container from said article after compacting.

2. A method according to claim 1 wherein said powdered metal is at an elevated temperature during compacting thereof.

3. A method accor-ding to claim 2 wherein said container is at a pressure substantially less than atmospheric during compacting.

4. A method according to claim 1 wherein said article is compacted to a density of at least about percent.

5. A method according to claim 1 wherein said contained is conned within a die during compacting.

6. A method according to claim 5 wherein said axial compressive force is applied by a ram that is inserted within said die to compress said charge of powdered metal.

No references cited.

BENJAMIN R. PADGETT, Primary Examiner. A. J. STEINER, Assistant Examiner. 

1. A METHOD FOR PRODUCING A COMPACTED ARTICLE FROM POWDERED METAL COMPRISING FILLING A CYLINDRICAL METAL CONTAINER HAVING HEMISPHERICAL ENDS WITH A CHARGE OF POWDERED METAL TO BE COMPACTED, APPLYING AXIAL COMPRESSIVE FORCE TO SAID CONTAINER TO COMPACT SAID CHARGE OF POWDERED METAL, RESTRICTING LATERAL SPREAD OF SAID CONTAINER DURING SAID APPLICATION OF AXIAL FORCE, AND REMOVING SAID CONTAINER FROM SAID ARTICLE AFTER COMPACTING. 